The objective of this study is to determine how flavin dehydrogenases interact with the membrane in Salmonella typhimurium. This work will focus on two main topics: 1. Regulation of the put operon. The put operon has a unique control mechanism that is mediated by the putA gene product. When exogenous proline is available, the PutA protein binds to the membrane where it functions as a flavin dehydrogenase; but in the absence of proline, it accumulates in the cytoplasm where it acts as an autogenous repressor. Determining how proline dehydrogenase controls its own expression may help us understand how other membrane-bound regulatory proteins work. In addition, the regulatory properties of putA mutations provide a genetic selection for membrane interaction mutants. 2. Flavin dehydrogenase-membrane interactions. Flavin dehydrogenases must associate with the membrane in order to interact properly with the electron transport chain. However, it is not known how they interact with the membrane or what components of the electron transport chain they interact with directly. Genetic studies on the interaction of PutA protein with the membrane provides a model system for understanding how proteins interact with membranes in vivo. The protein-protein and protein-lipid interactions required for membrane association can be determined by isolation of mutants that prevent the PutA protein from binding to the membrane. Genetic and biochemical analysis of these mutants will indicate what kinds of interactions are required between flavin dehydrogenases and the membrane electron transport chain. Such mutants should provide insight into the general biological problem of how peripheral membrane proteins interact with the membrane.